Alright, so we didn't see *that* coming - the fourth instalment of Fringe's final season ends on such a game-changing note that it left our fan-brain spiralling, desperately trying to work out where the show's remaining nine episodes can possibly go from here...

Those fans should have found what they were looking for with 'The Bullet That Saved the World' - there's plenty of action and gun-toting fun right from the off, as we see Peter (Joshua Jackson) delving deep into the dark dystopia on a personal mission. From there, the episode provides plenty more for longtime viewers to be happy about...

Fringe showrunner Joel Wyman has made it clear that this final season is really for the fans and that's more clear than ever in 'Bullet', which essentially equates to 42 minutes of fan service. And why not? After four years of sticking with the little sci-fi show that could, the fans deserve it.

So this week, Walter (John Noble) delves deeper in the amber encasing his old lab and unveils a secret "cold storage" room where he's been keeping 'souvenirs' from old Fringe cases, right under the nose of the FBI...

Wyman and his writing team manage to strike the tricky balance between servicing the fans and servicing the story. We get a few throwaway references to previous episodes - the porcupine man, the mirror portal into the other universe - but we also get to see an old favourite used in a new practical context, as our heroes launch an attack on the Observers using the rapid skin growth toxin from season one's 'Ability'.

But of course, the biggest fan-pleasing moment in 'Bullet' has to be the triumphant return of Lance Reddick as old favourite Broyles. As last season's flash-forward ep 'Letters of Transit' indicated, he's now boasting an impressive make-up job and is apparently in league with the Observers...

In fact, Broyles is simply smart enough to play the long game and is a member of the resistance, sending Etta (Georgina Haig) secret messages to protect her and the rest of the team. The moment when Broyles is reunited with his old allies is so sweet, particularly Reddick's gruff, perfect greeting to "Agent Dunham". We've missed Broyles - here's hoping that now he's back, he'll be sticking around for the long haul.

On a regular week, an action-packed assault and the dramatic return of Broyles would be more than enough to fill the running time of a Fringe episode. But events take a dark turn as 'Bullet' draws to a climax - Etta is trapped, alone and cornered by the sinister Captain Windmark (Michael Kopsa).

Killing off Etta is not only a surprise - newcomer Georgina Haig had been set up as a new series regular - but also an incredibly ballsy move. The character will still have a massive impact on the final season of Fringe, but not in the manner we'd anticipated.

At this point in the game, Etta had built up an openly warm relationship with her father, while Olivia's own interactions with her offspring remained adorably awkward. Both parents are stunned into silence at episode's end - we can only guess what the emotional ramifications of her demise will be. Right now, only one thing is clear - nobody and nothing is safe in this final season of Fringe.

• This week's Fringe glyphs spell out the word W O U N D

What did you make of 'The Bullet That Saved the World'? Leave your comments on the latest Fringe episode below!